1. FIELD OF THE INVENTION
The present invention relates to a process for producing a light-diffusing methacrylic resin article suitable as materials for light diffusion, for example, illuminated covers, illuminated signs, various displays, glazings, and rear projection, screens.
2. RELATED ART STATEMENT
As light-diffusing materials for illuminated covers, rear projection screens, and the like, which have heretofore been widely used, there are generally used materials produced by dispersing inorganic or organic, transparent, and fine particles in transparent synthetic resins.
In this case, as the transparent synthetic resins, there are used methacrylic resins, styrene resins, or vinyl chloride resins, and light-diffusion properties are attained by incorporating the transparent synthetic resin as substrate with, for example, inorganic transparent fine particles having an average diameter of 10 .mu.m or less of barium sulfate, calcium carbonate, quartz, etc., which have a refractive index different from that of the transparent synthetic resin, or by coating such inorganic transparent fine particles on the surface of transparent synthetic resin (see Jap. Pat. Appln. Kokai (Laid-Open) No. 54-155241, Jap. Pat. Pub. No. 46-43189, and Japanese Utility Model Registration Examined Publication No. 29-7440). There are also known light-diffusing materials obtained by including polymer fine particles obtained by copolymerizing substituted or unsubstituted styrene with a polyfunctional monomer, in place of the above-mentioned fine particles (see Jap. Pat. Pub. No. 39-10515, 46-11834 and 55-7471).
The resins disclosed in these prior art references are intended to improve the diffusion properties and are fairly effective. However, in recent years, sufficiently effective utilization of light has become important in the case of illuminated covers, displays, etc., because of the need of energy conservation.
When the quantity of light from a light source is constant, one of desired properties of a light-diffusing material is to diffuse light in a required direction, namely, directively, with a minimum of light absorption. On the other hand, when a directional light-diffusing material is used in instruments such as illuminated covers or displays, it is required to be formed into a shape suitable for these instruments. Examples of the suitable shape are shapes for surrounding light sources, flat plate having fine mat finished surface, and regular shapes such as lenticular lens shape and Fresnel lens shape.
Therefore, there is desired a material which not only possesses improved light-diffusion properties but also can easily be molded to the above shapes. But, conventional materials cannot be said to have directive light-diffusion properties, and even when they have directivity, they are disadvantageous in that a light source is seen through them.
Further, the production of a light diffusing resin by blending crosslinked polymer beads with a substrate resin is disclosed, for example, in Japanese Patent Application Kokai No. 61-159,440, etc. In said production, the blend of the crosslinked polymer beads with the substrate resin is extrusion-molded or injection-molded.
The above prior art aims to improve the light diffuseness of a resin and exhibits a proper effect. However, it has been impossible to impart to the resin a light diffusion ability to such an extent that a light source is not seen through the resin and transmittance is not greatly decreased. Particularly, in the case of the blend of the crosslinked polymer beads with the substrate resin, the decrease in transmittance is considered to be due to the reflection or absorption of light at the interface between the beads and the substrate resin.